Nonvolatile memories using deep traps formed in HfO2 by Nb ion implantation

We report nonvolatile memories (NVMs) based on deep-energy trap levels formed in HfO2 by metal ion implantation. A comparison of Nb- and Ta-implanted samples shows that suitable charge-trapping centers are formed in Nb-implanted samples, but not in Ta-implanted samples. This is consistent with density-functional theory calculations which predict that only Nb will form deep-energy levels in the bandgap of HfO2. Photocurrent spectroscopy exhibits characteristics consistent with one of the trap levels predicted in these calculations. Nb-implanted samples showing memory windows in capacitance¿voltage (V) curves always exhibit current (I) peaks in I¿V curves, indicating that NVM effects result from deep traps in HfO2. In contrast, Ta-implanted samples show dielectric breakdowns during the I¿V sweeps between 5 and 11 V, consistent with the fact that no trap levels are present. For a sample implanted with a fluence of 1013 Nb cm2, the charge losses after 104 s are 9.8 and~ 25.5% at room temperature (RT) and 85 degrees C, respectively, and the expected charge loss after 10 years is ~34% at RT, very promising for commercial NVMs